1. Field of the Invention
This invention relates to catalytic converters for exhaust-gas cleaning use, such as usable on the exhaust duct of a vehicular internal-combustion engine, and to methods of assembling same.
2. Description of the Prior Art
Generally, in a catalytic converter for vehicular use including a monolithic catalyst substrate, it is required that the substrate, which is relatively brittle in nature, be supported in the converter casing in shock-absorbing fashion so as not to be broken or damaged even under vibration or mechanical shock. This permits the catalytic converter to serve the intended cleaning function for an extended period of time while at the same time enabling it to be formed as compact as possible.
Conventionally, however, a catalytic converter of the type described includes, as illustrated in FIG. 4, a casing C' having a hollow cylindrical form of body 01 which is straight having the same diameter over the whole length thereof and in which a catalyst substrate 08, covered with a wire-mesh cushioning element 09 around the periphery thereof, is inserted while radially compressing the cushioning element. The catalyst substrate 08 inserted in casing body 01 and supported therein by cushioning element 09 is held axially in place by a pair of holding fixtures 011 fixed to the casing body and each fitted with an end cushioning element 010, which is engageable with the adjacent end face of catalyst substrate 08. With this construction, however, insertion into the casing body of the catalyst substrate 08 covered with cushioning element 09 has been more or less difficult and the cushioning element 09 has tended to be compressed to a higher density in its end regions (particularly in its forward end region with respect to the direction of insertion) than in the remaining intermediate region thereof. This means local increase in surface pressure acting on the catalyst substrate 08 and, when the catalytic converter is subjected to vibration or mechanical shock, local stress concentration may arise in the end regions of catalyst substrate 08 (particularly in its forward end region with respect to the direction of insertion), often causing damage or breaking of the catalyst substrate, which is brittle in nature.
Further, as the catalytic converter is subjected to repeated vibration or shock, the high-density end regions of cushioning element 09 gradually spread out axially outward and, coming into pressure contact with the end cushioning elements 010, force the latter outwardly thus to cause endwise play of the catalyst substrate 08 and hence early breakage thereof. As a measure to overcome this difficulty, it may be contemplated to provide between each end of cushioning element 09 and adjacent one of end cushioning elements 010 a space enough to keep these elements from abutting against each other. Such arrangement, however, must incur another sort of disadvantage of increase in total length and size of the casing C'.
A catalytic converter of the form described above has generally been assembled by the method which will be described below with reference to FIG. 5. In the figure, an insertion jig J' is shown fitted over one end of the straight form of hollow cylindrical casing body 07 and has an outwardly divergent flaring bore or opening whose smallest diameter A' is smaller than the inside diameter B' of casing body 07. The catalyst substrate 08, covered around the periphery thereof with cushioning element 09, is inserted axially through the insertion jig J' into the casing body 01 so as to be supported in the latter. In such conventional assembling method, however, the cushioning element 09 must be compressed by the insertion jig J' in excess of the amount of compression normally required. This means an undesirable increase in resistance to insertion of the catalyst substrate which causes certain assembling problems. Particularly, where the outside diameter of catalyst substrate 08 is held to a substantial tolerance, there is the danger of the catalyst substrate being broken at the time of its insertion into the jig J'. In addition, the unduly large insertion resistance must result in various assembling defects including dislocation of cushioning element 09 in relation to the catalyst substrate 08, nonuniformity in contact length of cushioning element 09 with the catalyst substrate, and early fatigue of cushioning element 09, which in combination incur early breakage of the brittle catalyst substrate 08.